Police said they received a ‘999’ call alerting them to a “mental health incident” around 05:33 this morning.
The Tunnel was subsequently closed in both directions by 05:42, with commuters urged to find alternative routes.
In total, 12 Police officers assisted by two Honorary Officers intervened to help safely detain the man.
The Tunnel was reopened at 08:13.
A spokesperson confirmed that the male, who was in his 40s, will now have a mental health assessment.
They added that no one was hurt during the process.